1. Field of the Invention
The present invention relates to a circular cylinder type piezoelectric actuator used in a positioning apparatus of a precision apparatus or the like, and is applied to, for example, a scanner or the like for a scanning probe microscope.
2. Description of the Related Art
In a background art, a circular cylinder type piezoelectric actuator is used in various precision apparatus starting from a scanning probe microscope as a fine positioning apparatus of order to several hundreds micrometers from sub-nanometers.
Here, a positioning apparatus using a circular cylinder type piezoelectric actuator will be explained by taking an example of a scanning probe microscope (refer to Patent Reference 1).
FIG. 11 is a constitution view of a scanning probe microscope of a background art, and FIG. 12 is a perspective view of a circular cylinder type piezoelectric actuator used as a 3 axes finely moving mechanism of the scanning probe microscope of FIG. 11. The scanning probe microscope of the background art is constituted by a cantilever 214 having a stylus 213 at a front end thereof, a sample holder 211 installed at a position opposed to the stylus 213 and mounted with a sample 212, a 3 axes finely moving mechanism 215 constituted by a horizontal direction finely moving mechanism for moving the stylus 213 relative to a surface of the sample and a vertical direction finely moving mechanism for moving the stylus 213 in a direction orthogonal to the surface of the sample, and a displacement detecting mechanism 219 for detecting bending of the cantilever 214.
According to the background art of FIG. 11, the circular cylinder type piezoelectric actuator 215 as shown by FIG. 12 is used at the 3 axes finely moving mechanism 215. A circular cylinder type piezoelectric element constituting the circular cylinder type piezoelectric actuator 215 is subjected to a polarization processing in a direction orthogonal to a center axis of a circular cylinder from an inner peripheral face in a direction of an outer peripheral face thereof. The inner peripheral face of the circular cylinder type piezoelectric element is formed with a single common electrode 232, and the outer peripheral face is provided with a strip electrode portion 235 provided along a circumference, and 4 divided electrode portions 233, 234 which are divided in 4 with regard to the circumference in a direction in parallel with the center axis. When a side of providing the strip electrode portion 235 is constituted as a front end and a side of providing the 4 divided electrode portions 233, 234 is constituted as a distal end, the front end is attached with the cantilever 214, and the distal end is fixed to a base (not illustrated).
According to the circular cylinder type piezoelectric actuator, the 4 divided electrode portions 233, 234 are operated as a horizontal direction fine moving mechanism, and the strip electrode portions 235 is operated as the vertical direction finely moving mechanism. When the circular cylinder type piezoelectric actuator is driven, the common electrode 232 of the inner peripheral face is connected to a ground potential, and voltages of inverse phases are respectively applied between two of electrodes of the 4 divided electrode portions 233, 234 opposed to each other relative to the center axis. At this occasion, one of the electrodes is elongated in a direction in parallel with the center axis, another one of the electrodes is contracted, as a result, bending is produced at the circular cylinder type piezoelectric element and the front end carries out a circular arc movement. Here, a moving amount of the circular arc moving is small, and therefore, the stylus 213 can be moved substantially in parallel with in-face of the sample 212. By making another one of two electrodes opposed to each other carry out a similar operation, the stylus 213 can be moved to two-dimensionally in-face of the sample 212.
Further, when a voltage is applied to the strip electrode portion 235 of the outer peripheral face, a strain is generated in a diameter direction, as a result, a strain is produced also in a direction in parallel with the center axis, and the stylus 213 can be moved in a direction orthogonal to the sample 212.
An optical lever method is generally used for the displacement detecting mechanism of the cantilever 214. The displacement detecting mechanism 219 is constituted by a semiconductor laser 216, a converging lens 217, and a photodetector 218. Light of the semiconductor laser 216 is converged to a back face of the cantilever 214 by the converging lens 217, and light reflected by the back face of the cantilever 214 is detected by the photodetector 218. When bending is produced at the cantilever 214, a position of a spot on the photodetector 218 is changed and bending of the cantilever 214 can be detected by detecting a change amount.
When the stylus 213 and the sample 212 are made to be proximate to each other by the scanning probe microscope constituted in this way, an atomic force or a contact force is operated and bending is produced at the cantilever 214. At this occasion, the bending amount depends on a distance between the stylus 213 and the sample 212, and therefore, the bending amount is detected by the displacement detecting mechanism 219 of the cantilever 214, the vertical direction finely moving mechanism is operated by a control circuit 221 such that the bending amount becomes constant, and while carrying out a feedback control such that the distance between the stylus 213 and the sample 212 becomes constant, by subjecting the horizontal direction fine moving mechanism to raster scanning by a scanning circuit 222, an image of recesses and projections of the sample surface can be measured. Further, other than the contact system of detecting a static bending of the cantilever 214, there is also a case of carrying out a measurement by a vibration system of controlling the distance between the stylus 213 and the sample 212 by a change amount of amplitude or a phase or a frequency by the atomic force or an intermittent contact force by vibrating the cantilever 214 at a vicinity of a resonance frequency.
Meanwhile, the 3 axes finely moving mechanism 215 used as the positioning apparatus of the scanning probe microscope is constituted by the piezoelectric element, and therefore, hysteresis or creep is produced. Hysteresis is a phenomenon in which when the voltage is applied to the piezoelectric element, the displacement does not become completely linear relative to the voltage but an operation similar to a quadratic curve is carried out. Further, creep is a phenomenon in which when a certain voltage is applied to a piezoelectric element, a target moving amount is not reached immediately but small movements are carried out little by little over time.
When the hysteresis or the creep is generated, it is difficult to carry out accurate positioning, and therefore, normally, the hysteresis or the creep is corrected by a previously set calibration equation. Further, according to the correction by the calibration equation, it is necessary to take various parameters of a scanning speed and a scanning angle or a scanning amount or the like into consideration and there is a case of producing an error depending on a drive condition, and therefore, there is also a case of compensating for the hysteresis or the creep by detecting a displacement of the positioning apparatus by using a displacement detecting apparatus of detecting a displacement of the piezoelectric element as a more accurate positioning means.
Although various systems of an optical type sensor or an electrostatic capacitance sensor, a magnetic type sensor and the like are used for the displacement detecting apparatus of the piezoelectric element, detection by a strain gage is effective as a method which occupies a space the least, is inexpensive and simple.
FIG. 12 shows a circular cylinder type piezoelectric actuator attached with a displacement meter of detecting a displacement of a 3 axes finely moving mechanism of a scanning probe microscope of a background art by the strain gage. According to the background art, strain gages 201a, 201b, 202a, 202b are adhered to the 4 divided electrode portions 233, 234 of the outer peripheral face of the circular cylinder type piezoelectric element 215 sheet by sheet to the respective electrodes. Further, 2 sheets of strain gages 203a, 203b are adhered to the strip electrode portion 235 in parallel with the center axis. The strain gage is a strain gage on sale generally, and is adhered in a direction of providing a large output when a strain is generated in a direction in parallel with the center axis of the circular cylinder type piezoelectric element. In a general strain gage, an insulating material of polyimide resin or paper, phenolic resin, epoxy resin, phenolic/epoxy mixture resin or the like is used for a base member, a resistance member constituted by a metal material of copper nickel alloy, nichrome species alloy or the like, or a semiconductor of a silicon single crystal or the like is provided on the base member, and is electrically connected to an outside detecting apparatus by way of an electrode pattern of nickel or the like formed on the base member similarly.
According to the horizontal direction finely moving mechanism, a bridge circuit as shown by FIG. 13 is integrated by respective 2 sheets of the strain gages 201a, 201b, 202a, 202b pasted on two electrodes 233, 234 opposed to each other and two of fixed resistors 241, 242, a bridge voltage e0 is applied to the bridge circuit, and an output voltage e1 is measured. When a strain is produced at the piezoelectric element, resistance values of the strain gages 201a, 201b, 202a, 202b are changed and a value of the output voltage e1 is changed. A strain amount of the piezoelectric element can be measured by detecting the output voltage e1. Further, according to the background art, respective 2 axial sheets of the gages 201a, 201b, 202a, 202b are adhered to the electrodes 233, 234 opposed to each other relative to the center axis, and therefore, directions of respective strains are reversed by bending the horizontal direction finely moving mechanism relative to the center axis, and therefore, also signs of detecting signals of the respective strain gages are reversed, an output voltage twice as much as that in a case of pasting the strain gage only to 1 sheet of the electrode can be provided and a signal intensity relative to noise is increased. Further, temperature compensation is also carried out by canceling an amount of a change of the resistance value in accordance with a change in a temperature.
Further, in the case of the vertical direction finely moving mechanism, a bridge circuit is integrated as shown by FIG. 14 by 2 sheets of strain gages 203a, 203b and two fixed resistors 241, 242, a bridge voltage e0 is applied to the bridge circuit, and the output voltage e1 is measured. When a strain is produced at the piezoelectric element, a resistance value of the strain gage is changed and a value of the output voltage e1 is changed. The strain amount of the piezoelectric element can be measured by detecting the output voltage e1. Also in this case, an output voltage twice as much as that of a case of 1 sheet of the gage can be provided. However, compensation of an amount of a change in the resistance value in accordance with a change in a temperature is not carried out in the circuit.
Further, according to the output of the strain gage, the displacement and the output voltage e1 are calibrated from data when a sample for calibration is measured by other displacement meter a displacement of which is previously calibrated and the scanning probe microscope using the 3 axes finely moving mechanism, and a displacement amount can be measured from the output voltage e1 provided.
In this way, a feedback control is carried out such that the 3 axes finely moving mechanism is linearly operated relative to an applied voltage from displacement information measured at any time from the output voltage of the strain gage in this way. Further, it is not necessarily needed to carry out linear operation relative to the voltage in the vertical direction according to the scanning probe microscope and there is also a case of displaying height information provided from the output signal of the strain gage as it is.
Next, FIG. 15 through FIG. 17 show a scanning probe microscope of other background art (refer to Patent Reference 2).
The background art relates to a scanning tunnel microscope using a circular cylinder type piezoelectric actuator which is a kind of a scanning probe microscope. FIG. 15 is a constitution view of the scanning tunnel microscope of the background art, FIG. 16 is a perspective view of a circular cylinder type piezoelectric element used as a horizontal direction finely moving mechanism in FIG. 15, and FIG. 17 is a sectional view taken along a line B-B of FIG. 16.
According to the background art, a 3 axes finely moving mechanism 305 is realized by integrating together 2 pieces of circular cylinder type piezoelectric elements of that for a vertical direction finely moving mechanism 314 and that for a horizontal finely moving mechanism 306.
A circular cylinder type piezoelectric element 308 as shown by FIG. 16 is used for the horizontal direction finely moving mechanism 306. The circular cylinder type piezoelectric element 308 is constituted by a structure of being provided with 4 divided electrode portions (309a, 309b, 310a, 310b) at an outer periphery similar to the horizontal direction finely moving mechanism of the preceding background art, and provided with a common electrode 311 in a strip-like shape at an inner peripheral face. Further, the vertical direction finely moving mechanism 314 is constituted by a structure of being provided with strip electrode portions (316, 317) respectively at an outer peripheral face and an inner peripheral face similar to the vertical direction finely moving mechanism of the preceding background art.
2 pieces of the circular cylinder type piezoelectric elements (308, 315) are arranged in a shape of concentric circles such that respective center axes thereof coincide with each other by arranging the horizontal direction finely moving mechanism 306 at an outer periphery and the vertical direction finely moving mechanism 314 at an inner periphery, 2 pieces of the circular cylinder type piezoelectric elements (308, 315) use a connecting member 312 in a cylinder shape and having a flange portion c, the flange portion c of the connecting member 312 is fixed to a front end of the horizontal direction finely moving mechanism 306, and the vertical direction finely moving mechanism 314 is fixed to a bottom face of an inner side of the cylinder.
Respective electrodes of the 4 divided electrode portions (309a, 309b, 310a, 310b) of the outer peripheral face of the horizontal direction finely moving mechanism 306 are connected with drive power supplies (320, 321) for respective electrodes, and connected such that polarities of the electrodes opposed to each other by interposing an center axis differ from each other, grounds of the respective drive power supplies (320, 321) are commonly connected and connected to the strip electrode 311 of the inner peripheral face.
Further, also the vertical direction finely moving mechanism 314 is connected with a drive power supply 322, the strip electrode 316 of the outer peripheral face is connected with a plus electrode of the drive electrode 322 and the strip electrode portion 317 of the inner peripheral face is connected with a minus electrode thereof.
Further, according to the background art, the outer peripheral face of the connecting member 312 is provided with a shield electrode 313, and the shield electrode is grounded.
A front end of the vertical direction finely moving mechanism 314 is provided with a probe holder 319, and the probe holder 319 is attached with a conductive stylus 318. A sample holder 303 is provided and a sample 304 is mounted at a position of being opposed to the stylus 318.
When a measurement is carried out by the scanning tunnel microscope, electrodes (309a, 309b) (310a, 310b) opposed to each other of the horizontal direction finely moving mechanism 306 are applied with voltages magnitudes of which are equal to each other and polarities of which differ from each other, and the circular cylinder type piezoelectric element 308 is deformed to bend, thereby, while subjecting the stylus 318 to raster scanning, an offset voltage is applied between the stylus 318 and the sample 304, and a recessed and projected shape of the sample 304 is measured while controlling a distance between the stylus 318 and the sample 304 by the vertical direction finely moving mechanism 314 such that a tunnel current which flows therebetween becomes constant.
At this occasion, although an electric field is changed by the voltage applied to the electrodes (9a, 9b, 10a, 10b, 11) of the horizontal direction finely moving mechanism 306 and electric noise is added to the vertical direction finely moving mechanism 314, according to the background art, by providing the shield electrode 313 to the connecting member 312 between the horizontal direction finely moving mechanism 306 and the vertical direction finely moving mechanism 314, electric noise generated in the horizontal direction finely moving mechanism 306 is prevented, and an excellent recessed and projected image can be provided.    Patent Reference 1: JP-A-9-89913    Patent Reference 2: JP-A-2002-55038
However, according to the circular cylinder type piezoelectric actuator of the background art constituted in this way, the following problem is posed.
The circular cylinder type piezoelectric actuator is integrated to inside of an apparatus of the scanning probe microscope. Inside of the apparatus is normally arranged with a wiring for driving the circular cylinder type piezoelectric actuator, a signal line of a displacement detecting signal of a cantilever, or in a case of using the displacement detecting apparatus of the piezoelectric element, a sensor or a wiring of the displacement detecting apparatus, further, in a case of detecting a physical property of the sample of an electric property or the like by the scanning probe microscope, a signal line or the like in a case of detecting the physical value in the form of surrounding an outer side electrode of the circular cylinder type piezoelectric actuator is arranged. Further, in a case of carrying out a measurement by a vibration system, a signal line used for oscillating a cantilever is arranged. Further, in order to make the sample and the stylus proximate to each other, or position in a measured portion of the sample in a sample face, there is a case of integrating an electromagnetic type stage for roughly moving in which an accuracy is rough and a moving amount is larger than those of the 3 axes finely moving mechanism.
When the circular cylinder type piezoelectric element is driven, a high voltage of several hundreds V order is normally applied, and therefore, a component of the high voltage applied to the outer electrode of the piezoelectric element is mixed to a part, a wiring member or the like surrounding the surrounding as noise. As a result, a measurement accuracy of the apparatus is deteriorated.
Further, there is also a case of mixing a signal of driving the electromagnetic motor of the roughly moving stage from an outer peripheral face electrode side of the circular cylinder type piezoelectric actuator as a noise component.
Further, when insulation of a part or a wiring member arranged at the outer side electrode of the circular cylinder type piezoelectric element is incomplete, there is a danger of destructing the apparatus by shortcircuiting the electrode of the outer peripheral face and the part or the wiring member surrounding the surrounding, or generating discharge in vacuum or the like.
Further, although according to the constitution of the scanning tunnel microscope of the background art, the electric signal of the horizontal direction finely moving mechanism can be prevented from being mixed to the vertical direction finely moving mechanism arranged at the inner periphery of the horizontal direction finely moving mechanism, the outermost periphery of the 3 axes finely moving mechanism is arranged with the 4 divided electrodes applied with the drive voltage, and therefore, electric noise cannot be prevented for a surrounding of the 3 axes finely moving mechanism.